<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <style>
    * {
      padding: 0;
      margin: 0;
    }

    .box {
      height: 600px;
    }

    #left {
      width: 300px;
      background: rgb(203, 59, 59);

      float: left;
      /*  */
    }

    #right {
      background: rgb(59, 169, 203);
      margin-left: 310px;
    }
  </style>
</head>

<body>
  <div id="layout">
    <div class="box" id="left"></div>
    <div class="box" id="right"></div>
  </div>
</body>

</html>